Vibration measuring device



y 13, 1952 F. CLARKE 2,596,531

I I VIBRATION MEASURING DEVICE Filed Dec. 9, 1949 Displacemenf 1 1?. 2 wITNE-SSESS I INVENTOR. W (I a r llBoyward FClarke Patented May 13, 1952 UNITED STATES PATENT OFFICE- 2,596,531 iiiisith fioh MEASURING DEV-ICE Hofiai-d 'F; 'olarke, ia'uuman, ss'sighorto the United States of Ameria as represehtedby the United smes'htomic Ehemgyoommhsmn Estimation Deaeinth 9, isia 's'eriai-tto. ittlit (outs -s1;

"6 claiiifsr present apphchtibh is in bait tbhtih ajti'on of r;bpending applications Serial No. 132,153 and 132,16; both filed Deca ters, 194 9.

This'invent-ion relates to appai'atus for meas and indicating small displacements, More specifically, the" invention relates toan eleotronie for measuring and indicating vishally the chafacterlstics of motion of vibrating mee s,

'A number of prioi" art arrangements are avail able for indioatihgby e'iotri bal means the chat afctei istics a; motion '0; 'vih i g bodies. n many such systems, anleotifo nieohanibal trahs= ieh tlvioeisfcofipled to t e fibre, ordito translate the physi'cfzal'quantities of vi b'i'a'tioh into electrical "quantities. sueh trans latfn'g devices geherany aie of the piezo-eleettie Oi" magiieto-i'fidtltiv'e type. In either case, a

direct physical conneoti on is necessitated between th' vibrating body and the Vibration Sensitive lmen; a: the translating devib. v 3

Other prio'rart devices utiliz'e li ght beam 'i' fiecti'on 'o'fi thevibrating bbjectand translate the light heam displacements into electrical ill-anti?- ties photo celi's. Devices of this type he hitficult in utilization e to the necessity of light shielding and elaborate apparatiis plaemnt.

It has been found that any for'mofdii'ect physital toup-ling between theobserved vibrating body and the translating element inherently creats a: h mbe; of deleterimijsfeffeots. Foremost among these is the Ina-ding effect on the vihrat'ing may with i'esultant modification of its hatiii'a l' vibratih'g thai'actei'istics.

pet-position of iesonance haracter'istics bfthe coupling link between the trahsiation element and the vibrating body on the vibration Charadtei'istios of the vibrating body per se. The iale'm trical quantities derived under these conditions ai not valid broportionalities to the motion of the observed body. h

Other disadvantages are present the pi'ioi' hiding adverse 'efig'ectsof 'v'ihra t a the fit; mg devibe rgr ihstanoe, the piezo elee t'ric translator is structurally delicate aha ifshb jii'td 170' even momentarily excessive vibration amplitudes, it is likely to fracture and, thus be rendered useless. addition, this'typ of transla'toi' ifs subjebt to deterioration due to envi'r o'nmental fefiectsfslfi'ch as for example, tem-peiaand humidity. The I magnetb induotive translator is also subj'ett to deterioration due to fatigue and the imposition of "stresses beyond the design value.

of tfib "fiisht invention, a 'iirhiiii'al hbfiit-is "th plvid e "a VibiQitiQh ihefls'iirih'g d'vit' WI-iibh the only coupling between the deviceahd the observed Object is aft emetic-magnetic field, in

3 which improved aoouracy is obtained thehieasuremen't of small displacements.

Other bhjec'tsieatures a a edvahtageswill abpjlf in the "fbllov'ling detailed desiiritiiih of a preferred emlo'odir'r'ient of the in'vhtibn. It be understood that this embodiment is only ah illustrative example of whence and that the hiventioh comfifehefrds "siich other em eaimehts-ah come Within the 500139 aimlspirit of th h'fipefided claims.

is In the aeconipahyihg thawing made a heft-bf this specification: j

Figure 1 illustrates a practical Eiiflioi'fihfi? in perspective partly in "section of the inventioii.

Figure 2 is a chart showing the relation: be-

I 20 tween potential developed by the apparatus oer responding to displacement of the observed oh J'ect.

Heret'ofore, in the referehced copenhfi'ns'athih cations, vibration measuring devices have been shown in which micYo-waves are injected into a wave guide, and emitted from an o en'ena thereof to impinge upon the'obseived vibrating "sur face. Part of the impinging energy is 'refi'btd back into the wave guide so that either the amiitude of reflected energy or the amplithde aha po'sitioh of standing waves In this wave guide a function of theinstantaneou's 'position bf "the observedsurfaoe. W In the present invfition, "a, miTO-W-ave 'gffici'e section of the ype known in'the art as them'agfi'o tee or T-bridg'e is used. This waveguide section.

has four arms. Energy is injected into'a first one of the arms and no energy 'isemitted from a second of the arms if the'loads presented to the third and fourth arms are equal. It follow'sthat if a -vibrating body is supported in opposition to the energy path or the third arm and a load equal to thevibra'tifi'g beds in its mean position terminates the 'hilfp aith of the fbtirtharm,

that energy is emitted from the 'seb'ond arm "co'r responding to displacement of "the vibrating fiom its mean position. Energy emitted from the secm i arm has "an instantaneous mag'hitdde which is a function of the'instantaheous pbsition of the vibrating-body.

Referring to Fi-gtire 1, a "Wave guide of the magic tee variety indicated generallyby the referehce numeral 9. Energy is injected mm the arm I0 andn'o 'eneigyis emittedfrom outputam It follows, therbfore, that among the dbl-Fests 55 It under the-cohditien that the t rm fi pedances presented to arms I2. and [3 are equal.

The vibrating body I4 is supported in opposition to the energy path of wave guide arm l2 so that at least a portion of the energy impinging thereon is returned into the wave guide. The opposite wave guide arm I3 is terminated by a tuned section l5 which is adjusted to reflect an amount of energy equal to that reflected by the vibrating body in a selected position. Deviations in the position of the vibrating body from the selected position are translated into variations in energy emitted from arm I l.

The magic tee section is energized by a microwave generator 20 which is coupled thereto through a tuned coupling section 2| and an attenuator section 22. The attenuator section is for the purpose of preventing variations in reflected energy in the magic tee section from being reflected back to the micro-wave generator as a variable load impedance. The attenuator section, therefore, prevents variations in generator output frequency and amplitude due to variations in position of the vibrating body I4.

Variations in amplitude of the micro-wave energy traversing magic tee arm II as a result of excursions of vibrating body M are converted into unidirectional potentials by detector 26. The unidirectional potentials are impressed on an indicator which can be an oscilloscope as shown at 28.

It has been found to be expedient to excite the vibrating object and the oscilloscope horizontal sweep from a common source. This is accomplished as shown schematically by coil 30 energized by a source 3|. The oscilloscope horizontal sweep is likewise energized by source 3| with the result that the instantaneous positions of the vibrating body are loci developing a single trace.

It has been found to be advantageous to energize the apparatus with wave energy of pulsed square wave form. The oscillator in the microwave generator 20 is preferably a klystron which is modulated half time on and half time off by a square wave generated by modulator 32. The square wave is inserted in series with the beam or reflector supply. The modulating energy is square wave rather than sine wave in order to prevent frequency modulation of the oscillator.

The wave guide detector is tuned and feeds into a tuned amplifier 34 which in turn ultimately feeds the vertical deflecting plates of the oscilloscope. The amplifier can be made very sensitive because it does not respond to spurious signals induced in the detector unless they are modulated at the modulation frequency.

The manner in which the apparatus is calibrated is explained with reference to Figure 2.

The observed body is first permitted to remain in its stationary unexcited position. The impedance I5 is tuned so that no energy passes to detector 28 and this establishes the point A on the curve of Figure 2. The observed bodyis next moved in measured increments toward or away from the mouth of the wave guide thereby determining the loci of all points of the curve B and the trace deflection values of the oscilloscope 2B are established. The point 0 is chosen as the center of symmetry and the observed body shifted in position so that in its stationary condition, it is positioned in a location corresponding to C on the abscissa of Figure 2. It follows that the observed object, if energized, vibrates from the mean position C so as to establish an approximately linear trace on the oscilloscope.

It is therefore seen that an apparatus has been described which is capable of indicating and measuring displacements of a vibrating body without mechanically interfering with the natural characteristics of the body.

Although the invention is described in the foregoing specification with reference to a preferred embodiment, other modifications are possible. Therefore, the invention is to be restricted only by the appended claims, as interpreted in view of the prior art.

What is claimed is:

1. In a device for measuring small displacements of an observed vibrating electric wave reflecting object, a magic tee Wave guide having first, second, third and fourth arms, said second and third arms being collinear, said first arm being normal to the second and third arms and in the same plane thereof and said fourth arm being normal to the plane of the first, second and third arms, means for injecting electromagnetic wave energy in the first of said arms, said second arm free end being open, means supporting the wave guide with the axis of the second arm adapted to intercept the observed object and with the open end thereof spaced from and proximate to said object, means for terminating the third arm with a dummy load, and rectifier means coupled to the fourth arm whereby a uniairec-' tional potential is generated corresponding to displacements of the observed object.

2. In a device for measuring small displacements of an observed vibratory object. a magic tee Wave guide having first, second, third and fourth arms, said second and third arms being collinear, said first arm being normal to the second and third arms and in the same plane thereof and said fourth arm being normal to the plane of the first, second and third arms, means for injecting electromagnetic wave energy into said first arm, said second arm having an open end, means for supporting the Wave guide second arm collinearly with and its open end proximate to the observed object, a rectifier coupled to the fourth arm and means for adjusting the impedance of the third arm so that no energy is impressed on the rectifier corresponding to a selected position of the observed object.

3. In a device for measuring vibrational'displacement of an observed object, a magic tee wave guide, said wave guide having first, second, third and fourth arms, said second and third arms being collinear, said first arm being normal to the second and third arms and in the same plane thereof and said fourth arm being normal to the plane of the first, second and thirdarms, means for injecting electromagnetic wave energy into the first of said arms, said second arm having an open end, means for supporting the vibratory object exteriorly of the second arm on the axis and proximate the open end thereof, means for terminating the third arm so as .to balance energy reflected into the second arm by the vibratory object in norm position, and rectifier means coupled to the fourth arm adapted to generate a potential corresponding to the instantaneous displacements of the observed object.

ing a T-bridge wave guide having an energy inlet arm, a first and a second side outlet arm and a terminal outlet arm, said first side outlet arm being open at its free end, an electromagnetic wave energy source, an attenuator wave guide section coupling the energy source and the wave guide inlet arm, said-T-bridge wave guide being 4. A displacement measuring device comprisadapted to be supported so that the energy path of the first of the side outlet arms intercepts an observed movable object, energy indicating means coupled to the terminal outlet arm and means for terminating the second side outlet arm with an impedance such that no energy is indicated by said indicating means for a selected position of said object.

5. A displacement measuring device comprising a T-bridge wave guide having an energy inlet arm, a first and a second side outlet arm and a terminal outlet arm, said first side outlet arm being open at its free end, a source of electromagnetic wave energy pulses, an attenuator wave guide section coupling the wave energy source and the wave guide inlet arm, said T- bridge wave guide being adapted to be supported so that the energy path of the first of the side outlet arms intercepts a moving object, a wave energy rectifier coupled to the terminal outlet arm and means for terminating the second side outlet arm with an impedance such that no potential is developed by said rectifier for a selected position of said object, an amplifier tuned to the frequency of occurrence of the wave energy pulses coupled to the rectifier, and an oscilloscope coupled to the amplifier.

6. A displacement measuring device comprising a magic tee electromagnetic wave guide having an energy inlet arm, a first and a second side outlet arm and a terminal outlet arm, said first side outlet arm being open at its free end, a source of electromagnetic wave energy pulses,

an attenuator wave guide section coupling the energy source and the wave guide inlet arm, said magic tee wave guide being adapted to be supported so that the energy path of the first of the side outlet arms intercepts an observed vibratory object, energy rectifier means coupled to the terminal outlet arm and means for terminating the second side outlet arm with an impedance such that no potential is developed by said rectifier means for a selected position of said object; an oscilloscope, an amplifier tuned to the frequency of occurrence of the wave energy pulses coupling the oscilloscope vertical deflection terminals to the rectifier means, a source of alternating current, motor means connected to said source of alternating current for vibrating the observed body and means for coupling the alternating current source to the oscilloscope horizontal deflection terminals to thereby obtain a synchronized trace.

HOWARD F. CLARKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,743,414 Wente Jan. 14, 1930 2,043,984 Alder June 16, 1936 2,403,289 Korman July 2, 1946 2,482,173 Hagstrum Sept. 20, 1949 2,498,548 Howard Feb. 21, 1950 

